If someone wants to pursue studies in Canada, they can do so only if they have applied for and granted study permit. You can even work on-campus or off-campus when you study for full-time program.
In order to legally work in Canada, you need a work permit. Most of the work permits are supported by LMIA but there are few exemptions to this prerequisite like spousal open work permit etc.
Citizens of many countries require a visitor visa to enter Canada and can stay up to maximum of 6 months per visit unless extension applied. However, there are few countries that do not require visa but still needs a Electronic Travel Authorization(ETA).
Under the visitor visa one can stay up to the maximum of 6 months per visit until you apply for extension. To overcome this, government of Canada has a Super Visa that let the parents/grandparents stay up to the maximum of 5 years per visit.